In this application we propose to investigate the biological features of a novel lymphoid population present in the intestinal epithelium. A hallmark of this population is the expression of CD8a and the production of cytokine/chemokine that indicate an innate immune phenotype. Therefore, we refer to this population as innate CD8a+ (iCD8a+) cells. Because of these features and their anatomical location within the intestinal epithelium, we hypothesize that iCD8a+ cells are a novel innate lymphoid population with an important biological function in mucosal immune responses of the intestine. In this proposal we will explore the biological role of iCD8a+ cells by primarily focusing on the phenotypic and molecular characterization of these cells, and their potential role in mucosal immune responses. For these purposes we propose the following complementary, yet independent aims: Aim 1. To assess the contribution of epithelial iCD8a+ cells in mucosal immunity. We will study the role on iCD8a+ cells in an acute model of intestinal inflammation induced by administration of anti-CD40 antibodies, with special emphasis on how these cells collaborate and/or influence other immune populations present in the intestinal mucosa, and the impact of these interactions during inflammation and colitis development. Aim 2. To characterize the lineage development and molecular expression profile of iCD8a+ cells. We will study the gene expression profile of iCD8a+ cells by using state-of-the-art next generation sequencing (RNA-seq) technology. The information obtained from this analysis will help us understand the lineage development of iCD8a+ cells and will further provide an indication of their putative role in mucosal immune responses. Successful completion of this project will provide important foundation for the understanding of the biology of iCD8a+ cells which will allow in depth characterization of this population in human tissue, and determine the impact of iCD8a+ cells on health and disease.